This invention generally relates to a system and method for controlling hub locks in a four-wheel drive vehicle and more particularly, to a system and method for controlling vacuum pulse hub locks in a four-wheel drive vehicle which employs an improved methodology that compensates for faulty operation and/or malfunction of the four-wheel drive control system.
Four-wheel drive vehicles typically include a transfer case which selectively transfers torque and power from the vehicle""s input shaft to primary and secondary driveshafts (e.g., rear and front driveshafts), thereby selectively rotating the primary and secondary driveshafts. The transfer case selectively operates in several different xe2x80x9cdrive modesxe2x80x9d, which determine the manner in which the transfer case delivers power to the primary and secondary driveshafts. These modes may include a two-wheel drive operating mode xe2x80x9c2Hxe2x80x9d, in which all of the torque from the input shaft is delivered to the primary or rear driveshaft, and one or more four-wheel drive operating modes (e.g., a four-wheel drive high mode xe2x80x9c4Hxe2x80x9d and low mode xe2x80x9c4Lxe2x80x9d), in which the transfer case provides torque to all four wheels.
Four-wheel drive vehicles also typically include xe2x80x9chub lockxe2x80x9d mechanisms which enable the front or xe2x80x9csecondaryxe2x80x9d wheels to be selectively connected and disconnected from the vehicle""s front or xe2x80x9csecondaryxe2x80x9d driveline. These hub lock mechanisms are activated as the vehicle is shifted from a two-wheel drive mode to a four-wheel drive mode, thereby allowing the torque from the front or secondary driveshaft to be communicated to the front or secondary wheels. These hub locks are often automatically actuated by use of a controller or control system. While these prior control systems can provide timely hub lock deployment, they suffer from some drawbacks.
For example and without limitation, these prior systems typically activate and deactivate (i.e., lock and unlock) the hub locks based upon the position of the vehicle""s transfer case motor. This motor is operatively coupled to an encoder which is communicatively coupled to a controller which selectively causes the shaft of the motor to occupy a certain desired position, thereby causing the transfer case to operate in one of the foregoing drive modes. The controller is communicatively coupled to the encoder assembly, effective to allow the controller to ascertain the motor position. Based on information received from the encoder, the controller is able to determine the position of the motor (e.g., whether the motor is in a position corresponding to a two-wheel drive mode or a position corresponding to a four-wheel drive mode), and thereby determine when to activate and/or deactivate the hub locks. Typically, communication between the encoder assembly and the controller occurs by the use of binary signals and binary codes representing different motor positions based upon a particular binary encoding methodology. These communications are prone to error and undesired malfunction or errant operation (e.g., errors or faults in the electrical communication often cause the controller to be incorrectly informed of the position of the motor). Hence, the information used to control the hub locks (e.g., the encoder reading) can be incorrect and can cause the hub locks to be locked or unlocked at inappropriate or incorrect times, thereby causing undesired binding, ratcheting and/or potential damage to the hub locks.
There is therefore a need for a method for controlling hub locks in a four-wheel drive vehicle which is effective to compensate for system faults, thereby preventing the undesired activation and/or deactivation of the hub locks.
It is a first object of the invention to provide a system and method for controlling hub locks within a four-wheel drive vehicle which overcomes at least some of the previously delineated drawbacks of prior systems, devices, and/or methods.
It is a second object of the invention to provide a system and method for controlling vacuum pulse hub locks in a four-wheel drive vehicle which compensates for faults within the vehicle""s transfer case control system, thereby ensuring that the hub locks are not undesirably activated or deactivated.
It is a third object of the invention to provide a system and a method for controlling hub locks within a four-wheel drive vehicle which detects faults within the vehicle""s transfer case control system and prevents the improper actuation of the hub locks in response to such a detection.
According to a first aspect of the present invention a system for controlling a hub locks assembly in a four-wheel drive vehicle having a transfer case which includes a motor which selectively causes the transfer case to operate in a plurality of operating modes, the system comprising: an encoder which is adapted to detect positions of the motor and to generate signals describing the detected positions; and a controller which is communicatively coupled to the hub locks assembly and to the encoder, the controller being effective to receive the signals and to selectively lock and unlock the hub locks assembly according to a certain control strategy based upon the signals, the controller being further effective to detect faults within the system and to selectively alter the control strategy based upon the detected faults.
According to a second aspect of the present invention a method for controlling a hub locks assembly in a four-wheel drive vehicle having a transfer case which includes a motor which is movable in a plurality of positions, effective to selectively cause the transfer case to operate in a plurality of operating modes, and an encoder which provides position readings corresponding to the position of the motor, the method comprising the steps of: selectively locking and unlocking the hub locks based upon the position readings; determining whether the motor is turned off; and ignoring position readings from the encoder indicating a changed position of the motor when the motor is off.
These and other features, aspects, and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.